The invention generally relates to measuring and testing. More specifically, the invention relates to the art of depth gauges and especially to methods and devices for determining volume of dry fluent materials. This invention provides a level sensor and control for sensing and controlling the level of particulate material within a storage bin. More particularly, a cable is suspended within the storage bin by a load cell whereby the weight of the cable can be determined and compared with the weight of the cable plus the force of particulate material within the storage bin on the cable to determine the amount of particulate material in the storage bin.
It is important to know the amount of particulate material in a storage bin for inventory purposes and to control the flow of the particulate material into and out of the storage bin. Often, the particulate material is caustic, corrosive, dusty, humid, clumpy, hot, and/or cold. Additionally, the particulate material may be crusted along the bin walls, may have hang-ups, an uneven top surface and cavitations or stalagmites caused by wet spots. In some cases steam is present. In grain silos, it also is important to measure the temperature at numerous locations within the silo to identify hot spots so that the grain can be agitated to minimize spoilage.
Many devices have been designed for the purpose of measuring the amount of particulate material in the storage bin. However, many are very expensive and cannot operate properly for long periods of time in the hostile environment described above. The most relevant prior art is discussed below.
McGookin U.S. Pat. No. 4,276,099 and McGookin U.S. Pat. No. 4,276,774 each disclose a device which senses both temperature and particulate material levels wherein the level of material within a silo is determined by weighing the portion of the cable above the level of the material by dropping the upper end of the cable so that there is slack in it whereby the weight of the cable above the material is weighed by a suitable scale and is compared to the total weight of the cable when the silo is empty.
Flickerstein et al. U.S. Pat. No. 4,910,878 is directed to a specific cam device for placing slack in the cable and measuring the weight of it.
Russian Patent No. S.U. 438,881 and French Patent No. 1,405,203 are each directed to a device for measuring the weight of the cable above the level of the material in a silo.
Each of these inventions is satisfactory for its intended purpose. However, each of them requires moving parts, such as a motor, for moving the upper end of the cable up-and-down so that measurements of the weight of the cable can be taken. This adds to the complexity, expense and chance that the device will fail after repeated use.
Other existing technologies are commercially available and used for level sensing. These are single point sensors such as: (1) a capacitance probe which senses if material is present around the probe; (2) a rotary shaft with paddles wherein the particulate material in the storage bin stops paddle rotation; (3) a lightly spring-loaded diaphragm which triggers a proximity switch in response to particulate material pressure on the diaphragm; and (4) a tilt switch, which is normally vertically hanging, having a probe which is pushed laterally, i.e., tilted by the particulate material pressure on the probe.
While single point sensors are relatively inexpensive, it is difficult to determine or calculate the correct load to position the single point sensors due to the stored particulate material""s angle of repose, moisture content, foreign material content, etc. For the diaphragm type single point sensor, it is necessary to cut a hole in the sidewall of the storage bin to install it. If the installer selects the wrong location, another hole must be cut in the tank to reposition the sensor and the electrical connections must be redone.
Additionally, there are continuous sensors such as: (1) sonic sensors which emit sound waves, measure the time for the sound wave to return, translate this difference in time into a distance and use digital signal processing algorithms to process the returned signal for a true signal, minimizing background noise; (2) radar sensors which use a high frequency signal traveling on a transmission line to measure empty space in the silo; and (3) a plum bob dropped from a spooling device which measures the distance that the plum bob moves. These continuous sensors are very expensive and can be adversely affected by the harsh conditions within the storage bin thereby requiring frequent maintenance.
The present invention is directed to a sensor for measuring the level of free-flowing particulate material in a storage bin. The sensor comprises an electronic load cell fixedly positionable at the upper end of the storage bin and having the upper end of the cable attached thereto to suspend the vertical cable in the storage bin so the lower end of the cable is adjacent to lower end of the storage bin. The load of the cable alone provides a signal indicative of an empty storage bin, and the load of the cable plus the downward force of any particulate material in the storage bin on the cable causes the electronic load cell to provide an output signal proportional to the amount of particulate material in the storage bin. A signal readout device is responsive to the output signal to provide a readout indicative of the amount of particulate material in the storage bin. One or more thermocouples may be attached along the cable to provide a signal indicative of the temperature of the particulate material at the location of the thermocouple.
The signal readout devices may include a process controller for receiving the output signal, for providing a low storage bin level output signal when the level of the particulate material in the storage bin falls below a predetermined low level, and for discontinuing the low storage bin level output signal when the level of the particular material in the storage bin exceeds a predetermined high level. A conveyor assembly or any kind of material supply system can be located adjacent to the storage bin. Such supply system is activated by the low level storage bin output signal to provide particulate material to the storage bin when the level of particulate material in the storage bin falls below the predetermined low level. The supply system is deactivated when the low storage bin level output signal is discontinued by the process controller, such as when the level of the particulate material in the storage bin reaches or exceeds the predetermined high level.
The process controller, which includes a clock, also can provide a real time readout of the rate of discharge of the particulate material from the storage bin. Since the process controller can be located at any remote location, this discharge rate can be monitored anywhere.